This invention relates to the treatment of "sour" petroleum and coal liquefaction hydrocarbons containing hydrogen sulfide and other organosulfur compounds such as thiols and thiocarboxylic acids, and more particularly, to improved methods of treating such streams by using aminocarbinols.
Petroleum and synthetic coal liquefaction crude oils are converted into finished products in a fuel products refinery, where principally the products are motor gasoline, distillate fuels (diesel and heating oils), and bunker (residual) fuel oil. Vacuum distillation towers separate the crude into narrow boiling fractions. The vacuum tower cuts deeply into the crude while avoiding temperatures above about 800.degree. F. which cause thermal cracking. A catalytic cracking unit cracks high boiling vacuum gas oil into a mixture from light gases to very heavy tars and coke. In general, very heavy virgin residuum (average boiling points greater than 1100.degree. F.) is blended into residual fuel oil or thermally cracked into lighter products in a visbreaker or coker.
Overhead or distillate products in the refining process generally contain very little, if any, hydrogen sulfide (H.sub.2 S), but may contain sulfur components found in the crude oil, including mercaptans and organosulfides. However, substantial amounts of hydrogen sulfide, as well as mercaptans and organosulfides, are found in the vacuum distillation tower bottoms, which may be blended into gas oils and fuel oils. In addition, hydrogen sulfide is produced during catalytic cracking or coking of higher boiling fractions and vent streams from those operations and from other refining operations must be treated to remove the hydrogen sulfide.
As employed in this application, "hydrocarbons" is meant to include the unrefined and refined hydrocarbonaceous products derived from petroleum or from gasification or liquefaction of coal, both of which contain sulfur compounds. Thus, the term "hydrocarbons" includes, particularly for petroleum based fuels, sour natural gas, casinghead gas, wellhead condensate, and crude oil which may be contained in storage facilities at the producing field and transported from those facilities by barges, pipelines, tankers, or trucks to refinery storage tanks, or, alternatively, may be transported directly from the producing facilities through pipelines to the refinery storage tanks. The term "hydrocarbons" also includes refined products, interim and final, produced in a refinery, including distillates such as gasolines, distillate fuels, oils, and residual fuels.
Hydrogen sulfide in natural gas or in refinery gases or which collects in vapor spaces above confined hydrogen sulfide containing hydrocarbons (for example, in storage tanks or barges) is poisonous, in sufficient quantities, to workers exposed to the hydrogen sulfide. Mercaptans are strongly malodorous. Refined fuels must be brought within sulfide and mercaptan specifications for marketability. In the processing of hydrocarbons, it is desirable to eliminate or reduce atmospheric emissions of noxious hydrogen sulfide, mercaptan or other sulfhydryl compounds associated with sulfur containing hydrocarbons, in order to improve environmental air quality at refineries.
Numerous proposals have been made to sweeten sour distillate products and to scrub hydrogen sulfide from sour gases by treatment with a variety of amine derivatives or other additives. Disclosures illustrative of these are contained in U.S. Pat. Nos. 4,997,630 (methyldiethanolamine); U.S. Pat. No. 4,978,512 (reaction product of monoethanolamine and formaldehyde); U.S. Pat. Nos. 4,957,715; 4,883,601; 4,764,354; 4,575,455; 4,557,991 (alkanolamines generally); U.S. Pat. No. 4,551,158 (methyldiethanolamine); U.S. Pat. No. 4,421,725(tertiary alkanolamine); and other processes involving the use of alkanolamines: U.S. Pat. Nos. 4,406,868; 4,205,050; 4,096,085; 4,085,192; 4,079,117; 3,685,960; 3,681,015; 3,516,793; 2,600,328; and 2,589,450. In gas scrubbing where alkaline aqueous scrubbing solutions normally are employed, alkanolamines are employed because of their solubility in water and alkalinity. In U.S. Pat. No. 4,405,585, a sterically hindered secondary aminoether alcohol was employed to selectively scrub hydrogen sulfide gas from a gaseous mixture of hydrogen sulfide and CO.sub.2. Dimethylaminoethanol and dimethylisopropanolamine were employed in U.S. Pat. Nos. 4,490,275 and 4,430,196 to neutralize acidic components in petroleum refining units. U.S. Pat. No. 5,030,762 suggests a quaternized adduct of formaldehyde and a secondary amine is useful for absorption of sulfur compounds produced by combustion of hydrocarbon materials.
The prior art relating to the treatment of sour petroleum oils also includes methods in which choline base has been employed to treat sour heavy fuel oils to maintain the hydrogen sulfide content in the atmosphere above or associated with such oils at levels within acceptable limits to avoid health hazards to personnel, as disclosed in U.S. Pat. No. 4,867,865. Choline base also has been used to treat gasoline and other motor fuels to remove organosulfur compounds such as thiols, thiolcarboxylic acids, disulfides and polysulfides, as disclosed in U.S. Pat. No. 4,594,147.
The use of choline base for these purposes has its drawbacks. Choline base itself has a strong unpleasant odor, and at low mix conditions has limited oil solubility. In the presence of water, choline base, like the alkanolamines described above, tends to seek the water in preference to oil, and does not distribute easily and thoroughly in oil without high mixing conditions. For example, it is recommended added by injection into the suction side of the product pump. Especially, this is a problem with fuel oils and residual oils. These heavy, high boiling fuels do not normally flow well at ambient temperatures, and heating at temperatures above about 140.degree. F. and high mix conditions are necessary to mix choline base into them. High mix conditions do not always exist, or may not be feasible, and a better way to treat hydrocarbons remains a challenge in order to reduce hazards of hydrogen sulfide exposure to workers, to bring fuels within sulfide or mercaptan specifications, and to eliminate or reduce atmospheric emissions of noxious hydrogen sulfide, mercaptan or other sulfhydryl compound odors associated with such fuels for improved environmental air quality.